1. Technical Field
This invention relates generally to a method and apparatus for controlling the length of liquid-phase fuel penetration into the combustion chamber of a direct-fuel injected engine, and more particularly to such a method and apparatus in which liquid fuel is controllably heated prior to injection into the engine combustion chamber to alter the liquid-phase penetration distance of the fuel.
2. Background Art
The performance of both spark ignition and compression ignition engines, and variations thereof, is generally improved by the use of controlled fuel injection into the combustion chamber, or more commonly into multiple combustion chambers, of the engine. Controlled fuel injection enables precise regulation of fuel flow quantity and injection timing, thereby providing better control of the combustion event for optimum efficiency and emissions reduction.
Several approaches have been proposed for controlling the combustibility of injected liquid fuels. For example, U.S. Pat. No. 6,125,818 granted Oct. 3, 2000 to Yoshio Okamoto, et al. for FUEL INJECTOR AND INTERNAL COMBUSTION ENGINE HAVING THE SAME, describes a direct injection spark ignition engine fuel injector directed to improving the combustibility and ignitability of the injected fuel. The proposed fuel injector uses multiple fuel swirl methods to produce a complex fuel spray pattern having a first fuel spray with a large spread angle and weak inertia force, i.e., a short penetration distance, and a second fuel spray that has a small spread angle with strong inertia force. The first fuel spray purportedly provides superior combustibility characteristics and reduced levels of unburned gaseous emissions. The second fuel spray pattern is purported to provide improved ignitability because the fuel with high inertia force collides vigorously with the piston cavity and is redirected towards the ignition plug.
Other methods for controlling the combustibility and/or ignitability of injected liquid fuel have been directed to control of the size of fuel droplets discharged from the fuel injector. For example, U.S. Pat. No. 5,626,115 granted May 6, 1997 to Akio Kawaguchi for a COMPRESSION-IGNITION TYPE ENGINE proposes controlling the fuel droplet size based on the theory that large fuel droplets injected during the intake stroke or early in the compression stroke of the combustion cycle will take longer to heat up than smaller fuel droplets. The mean particle size of the injected fuel is adjusted to a size in which the temperature of the fuel particles reaches the boiling point of the fuel at top dead center (TDC) of the compression stroke. In this manner, the fuel droplet vaporizes and is ignited and burned at approximately TDC.
Another approach to controlling fuel combustibility by regulation of fuel droplet size is disclosed in U.S. Pat. No. 6,006,720 granted Dec. 28, 1999 to Hiromichi Yanagihara, et al. for an INTERNAL COMBUSTION ENGINE proposes controlling the time-temperature history of a fuel droplet from a direct injection event by controlling the droplet size at the time of injection. This is accomplished by increasing the fuel droplet size, which in turn will slow the droplet heat-up relative to the bulk gas temperature during the compression stroke. The goal of this patent is to reduce the temperature rise rate of the fuel droplets during the compression stroke so that the fuel does not enter the “cool flame region” and prematurely initiate aldehyde formation.
However, none of the above methods of regulating the combustibility, ignitability, or volatility of injected fuels are directed to controlling the liquid-phase penetration depth of liquid fuel injected into the combustion chamber of an engine. Liquid fuel that remains on combustion chamber surfaces after the combustion event does not participate in the normal combustion process. It is generally wasted. Therefore, reduction or prevention of liquid fuel impingement improves fuel conversion efficiency. Furthermore, since liquid fuel remaining on combustion chamber surfaces does not undergo complete oxidation, these products can exit the combustion chamber as unburned hydrocarbons. Therefore, the prevention of liquid fuel impingement on combustion chamber surfaces will contribute to a reduction in output levels of regulated emissions. In addition, engine lubricant dilution can be reduced or prevented, since liquid fuel deposited on the combustion chamber surfaces can is able to mix with and dilute the engine lubricant, potentially degrading lubricant performance.
The present invention is specifically directed to overcoming the above-described problems associated with liquid fuel impingement onto combustion chamber surfaces. It is desirable to have a method, and an apparatus for carrying out the method, that provides control of the penetration distance of liquid-phase fuel from the fuel injector into the combustion chamber of direct injection engines. It is also desirable to have such a method and apparatus that enables the control of liquid-phase penetration distance that is able to compensate for real-time changes in fuel composition, injector geometry, injection pressure, combustion chamber thermodynamic conditions, or other engine operating parameters that lead to liquid fuel impingement on combustion chamber surfaces.